This invention relates to ultrasonic inspection of steel shafts and more particularly to ultrasonicly inspecting large diameter shafts from bores filled with a liquid.
When ultrasonics are utilized to inspect a large mass of metal, a liquid film is used as a medium to transmit ultrasonic sound from the transducer into the metal, however, when only a thin film separates the transducer or sonic lens from the metal, near surface flaws are often not distinguishable. By moving the transducers a greater distance from the surface, indications of sonic reflections near the surface may become more distinguishable. Since in shafts rotating at high speeds the area adjacent the bore is highly stressed and imperfections in this area will affect the life of the shaft, an inspection system should have good resolution near the bore and this may be accomplished by moving the transducer away from the bore surface improving the near bore resolution of sonic reflectors.
Large shafts such as in turbine and generator rotors are expensive to manufacture and because of their expense spare rotors are usually not available. The inspection of such rotors require a large amount of machinery down-time and if the rotors must be shipped to a special inspection location down-time is even greater. A system developed by Southwest Research Institute in joint sponsorship with the Electric Power Research Institute called Turbine Rotor Examination Evaluation System, TREES, uses twelve focus search transducers to determine flaw size. The transducers are utilized in a liquid-filled bore. Though the literature says the unit is enclosed in a portable container for easy transportation to field sites, the container is not expandable to provide an enclosed work station at the side of the inspection.